In large dairies, cows are typically milked in milking parlors in which several cows are milked simultaneously. When one group of cows has finished milking, that group is let out of the parlor and another group of cows is let in to be milked. The milk from each cow is typically drawn from the teat cup cluster--attached to the cow's udder--through a milk hose to a common milk pipeline which is under a vacuum draw. The milk from several cows is drawn through the pipeline to a common receiver tank where the milk is discharged from the pipeline into the tank. The receiver tank is connected to a vacuum pump so that the interior of the receiver tank is under vacuum pressure, thereby drawing the milk from the milk pipeline into the receiver tank. Periodically, the milk from the receiver tank is pumped by a milk pump through pipelines to a large bulk tank where it is held and cooled while awaiting transfer to a milk tank truck. The receiver tank is typically mounted in the parlor at the end of the common milk line, whereas the bulk tank is usually located in another room or building which is typically a substantial distance away from the cows in the milking parlor. In the typical double-herringbone milking parlor, a receiver tank and milk pump are located in the parlor at the end of the milk line on each side of the parlor.
When all of the cows in the herd have completed milking, the milking equipment and pipelines must be cleaned and sanitized before the next shift of milking begins. Commonly, a wash line is installed above the milking stations at which the cows are milked. When the milking shift has been completed, the dairyman typically connects the teat cups in the teat cup cluster to a clean-in-place unit washer or a wash manifold which is connected by a hose to the wash line. Wash water mixed with sanitizing chemicals in a wash tank or sink is then supplied to the wash line, through the clean-in-place manifold, the teat cups and the milk hose to the milk line; the wash water in the milk line is then drawn back to the receiver tank and pumped back by the milk pump through the pipelines that extend to the bulk tank. Bypass valves are opened to allow the wash water to recirculate rather than being passed into the bulk tank, and the recirculated water is eventually discharged to a drain. A connection may be made between the wash line and the milk line through a valve which is opened to provide some direct flow of wash water from the wash line to the milk line to provide a more thorough cleaning of the milk line.
In some systems, a separate wash water holding tank is provided in addition to the receiver tanks and the wash sink. The wash tank holds a large quantity of hot wash water and sanitizing chemicals. A pump is connected to the wash tank to pump the wash water into the wash lines. The relatively large capacity of the wash tank combined with the pressure applied to the wash water by the pump allows a vigorous flow of wash water to be provided to the wash lines and thence to the various milk pipelines to thoroughly clean the pipelines. To obtain enhanced cleaning action, air injector systems have been developed which allow air to be injected into the wash lines so that the wash water is driven along in "slugs" separated by air pockets to enhance the scrubbing and cleaning action of the wash water.
While such conventional washing systems adequately clean the various milk pipelines and related equipment, the washing lines and equipment add significant costs to milking parlor construction. The wash lines, wash sinks, wash tanks, receiver tanks, connectors and other equipment typically are formed of expensive stainless steel to ensure maximum cleanliness and durability. The milk pumps provided at the receivers which are located at the end of each milk pipeline for each side of the parlor must be of the highest quality. In addition to the significant capital cost of the long lengths of washing pipeline that are required for typical milking systems, the number of pipes through which the wash water must pass and the length of the pipes results in significant loss of heat from the hot wash water passing through the pipes, with the result that operating costs for hot water heating are significant. The space within the milking parlor that is physically occupied by the various wash lines also constrains the design of the parlor and reduces the space available for other equipment within the parlor. The long lines and the capacitors of the receiver tanks and wash tank has also required that large amounts of wash water be used during the wash-up process, which is a significant concern in areas where water is rationed or particularly expensive.
Some milking parlors have been installed in which the receiver tanks at the end of each of the two milk lines (for a double sided parlor) have been eliminated, and the large wash water holding tank has been employed also to serve as a receiver tank during milking. In these parlors, each of the two milk lines was connected to a single common line that extends to the wash/receiver tank. A milk pump is used to pump the accumulated milk from the wash/receiver tank to the bulk tank. During wash-up, a separate wash pump is used to pump wash water from the wash/receiver tank through the wash lines and the milking units and back through the milk lines to the wash/receiver tank. Because of the relatively long distance between the milking units and the wash/receiver tank (typically located outside of the milking parlor) difficulties may be encountered in obtaining adequate vacuum draw on the milk in the lines leading to the wash/receiver tank, particularly where the common milk line enters the receiver tank below the level of accumulated milk in the tank or where it enters at a higher level but with the requirement for a vertical section of milk pipeline through which milk must be drawn against gravity.